Conventionally, as a method for removing and reducing a thermal ingredient from light of an external light source such as sunlight, a beam of a bulb, or the like, a film containing a material for reflecting an infrared ray which greatly contributes to a thermal effect is formed as a heat wave reflecting transparent substrate on a surface of a transparent substrate such as glass or the like, and the heat wave reflecting transparent substrate is used. A metal oxide such as FeOx, CoOx, CrOx, TiOx, and the like, or a metallic material containing a large amount of free electrons such as Ag, Au, Cu, Ni, Al, and the like is used as the aforementioned material.
However, the aforementioned material has such properties to reflect or absorb not only the infrared ray which greatly contributes to the thermal effect but also a visual light at the same time, and therefore, there is a problem about lowering a visible light transmittance. However, since the transparent substrate such as glass or the like used for a window material such as a building material, a vehicle, a telephone booth, or the like requires a high transmittance in a visible light region, a film thickness thereof needs to be extremely thin when the aforementioned material is used. Accordingly, when the aforementioned material is formed on the transparent substrate, generally, a film having a thickness of as thin as approximately 10 nm is formed by physical film-formation methods such as spray baking, a CVD method, a sputtering method, a vacuum deposition method, and the like.
However, these film formation-methods require a huge apparatus or a vacuum equipment, and there is a problem of productivity or area enlargement, and a disadvantage of high manufacturing costs of the film. Furthermore, when a sunlight shielding characteristic (a characteristic for shielding a light having a wavelength band of 300 to 2100 nm) of the aforementioned material becomes high, reflectivity of the visual light region tends to be high at the same time, resulting in disfigurement caused by a glaring appearance like a mirror.
In order to improve the aforementioned problems, a sunlight shielding solid which exhibits the high visible transmittance and a high sunlight shielding rate is required to be formed on the transparent substrate or in the substrate. Furthermore, properties such as little haze of the film or the like are required for the sunlight shielding solid used for, for example, the window material or the like in addition to the aforementioned optical characteristics and electrical characteristics. The haze of the film is evaluated by a numerical value called a haze value. The haze value is defined as a ratio of a diffuse transmission light to a total transmittance, and the sunlight shielding solid looks hazy to human eyes when the value is high. Accordingly, the window material or the like requiring for transparency is desired to have the low haze value of less than 1%.
Here, an antimony tin oxide (hereinafter abbreviated as ATO) is known as one of the materials having a visible light transmittance function and a sunlight shielding function. However, physical characteristics of the ATO which exhibits the excellent visible light transmittance function and sunlight shielding function have never been studied, and for example, each of the ATO described in Patent Document 1, Patent Document 2, Patent Document 3, and Patent Document 4 relates to conductivity.    (Patent Document 1) Japanese Patent No.2844011    (Patent Document 2) Japanese Patent Laid-open No. Hei 11-278826    (Patent Document 3) Japanese Patent Laid-open No. Hei 6-183708    (Patent Document 4) Japanese Patent Laid-open No. Hei 5-246710
Here, the present invention clarifies the physical characteristics of the ATO capable of forming the sunlight shielding solid having such optical properties as the high visible light transmittance, a low solar radiation transmittance, and simultaneously the low haze value when the ATO is formed on the transparent substrate or incorporated in the substrate so as to be formed as a board shape, a sheet shape, a film shape or the like; furthermore, an object of the present invention is to provide ATO fine particles having the physical characteristics thereof, a disperse liquid for formation of a sunlight shielding solid which can form the sunlight shielding solid by a simple coating method or incorporating method, and the sunlight shielding solid containing the ATO which has the physical characteristics thereof.